i know where the problem come from.
when you use direct material assignation throw geometry loader input pin, the houdini reader work fine.
but when you use a material map assignment, the houdini reader is not able to read it.
so i think it is just that at the moment the orbx reader in houdini is not able to understand the material map node.
The big advantage of material map, is that when you update the geometry on an object with 15 shader assign, you just have to replace one connection.
When you use direct assignemnt if you modify the loader you have to reconnect all the 15 shader.
I find them pretty useful.